1. Field of the Invention
This invention relates to devices employing a nonlinear optical medium to affect, either by reflection or refraction, at least a portion of an incoming beam to reduce the illumination of an object. This invention particularly relates to such devices which are resonator optical bistable devices and to laser hardening applications of the invention.
2. Prior Art
Various devices have been proposed to reduce the amount or limit the frequencies of light irradiating an object. U.S. Pat. No. 3,792,916 to D. S. Sarna discloses a filter assembly for selectively removing preselected individual emission lines of laser energy from the visible spectrum wherein the filter comprises at least one pair of Fabry-Perot type filters which transmit laser energy emissions for dissipation in the filter assembly and reflect harmless radiation for transmission through the assembly.
U.S. Pat. No. 3,495,893 to J. E. Geusic, et al discloses a passive optical limiter utilizing the nonlinear transmission characteristics of a multiphoton absorbing material.
E. W. Deeg in U.S. Pat. No. 4,035,527 discloses optical elements comprising materials possessing phototropic or photochromic properties which are particularly adapted for use with sunglasses. Relatively long exposure times are required for the optical effects of Deeg's devices to occur.
H. M. Bolz in U.S. Pat. No. 3,062,103 provides a filter arrangement for passing a narrow range of wavelengths from a radiation beam containing a relatively broad range of wavelengths. The beam impinges obliquely on the surface of the filter medium having a strong absorption band so that total internal reflection takes place only within the range of anomalous dispersion. Within the range of anomalous dispersion, the absorbing filter medium has a lower index of refraction than the adjacent medium so that total reflection takes place at the interface if a suitable angle of incidence is chosen. The rest of the radiation passes in a refracted condition through the interface.
R. R. Austin U.S. Pat. No. 3,578,848 discloses a Fabry-Perot type interference filter in which the two reflectors are identical high reflection coatings that are separated by a spacer element made of solid glass.
It is highly desirable to provide means and methods of protecting an object from high intensity light when changes in the light intensity can occur very quickly. The prior art does not disclose means or method employing an intensity dependent, ultra fast optical switching effect to protect an object from an incoming light beam of high intensity.